Total knee replacement prosthesis with high order NURBS surfaces

Abstract

A knee replacement prosthesis comprising a femoral component and a tibial component that enable anterior-posterior translation of the femur relative to the tibia and enable the tibia to rotate about its longitudinal axis during flexion of the knee. The femoral component connects to the distal end of a resected femur and includes medial and lateral condyles having distal, articulating surfaces, and a patellar flange having a patellar articulating surface. The tibial component connects to the proximal end of a resected tibia and includes a proximal bearing surface with medial and lateral concavities that articulate with the medial and lateral condyles. The condylar articulating surfaces and the said concavities are substantially defined by non-uniform, rational B-spline surfaces (NURBS).

The invention claimed is: 
     
       1. A knee replacement prosthesis having anterior, posterior, lateral, medial, distal and proximal sides and sagittal, coronal and transverse planes, comprising:
 a) a femoral component that connects to the distal end of a resected femur, said femoral component including medial and lateral condyles having distal, articulating surfaces, and a patellar flange having a patellar articulating surface; and, 
 b) a tibial component that connects to the proximal end of a resected tibia, said tibial component including a proximal bearing surface with medial and lateral concavities that articulate with said medial and lateral condyles; 
 wherein said condylar articulating surfaces and said concavities are substantially defined by non-uniform, rational B-spline surfaces that enable anterior-posterior translation of the femur relative to the tibia and enable the tibia to rotate about its longitudinal axis during flexion of the knee. 
 
     
     
       2. The knee replacement prosthesis recited in  claim 1 , wherein axial tibial rotation is substantially restricted during initial flexion to an intermediate position, but is enabled after the prosthesis has been flexed beyond the intermediate position to full flexion. 
     
     
       3. The knee replacement prosthesis recited in  claim 2 , wherein the tibia rotates more than about 10 degrees axially after the prosthesis is fully flexed. 
     
     
       4. The knee replacement prosthesis recited in  claim 1 , wherein the condyles translate posteriorly in the concavities during flexion and anteriorly during extension. 
     
     
       5. The knee replacement prosthesis recited in  claim 4 , wherein the posterior translation is about 1-2 millimeters after the prosthesis is fully flexed. 
     
     
       6. The knee replacement prosthesis recited in  claim 1 , wherein said tibial concavities have multiple radii of curvature. 
     
     
       7. The knee replacement prosthesis recited in  claim 6 , wherein said tibial concavities have at least a first radius of curvature in the sagittal plane and at least a first radius of curvature in the coronal plane that is larger than the sagittal radius of curvature. 
     
     
       8. The knee replacement prosthesis recited in  claim 7 , wherein said concavities have multiple radii of curvature in the sagittal plane. 
     
     
       9. The knee replacement prosthesis recited in  claim 1 , wherein said condylar articulating surfaces have multiple radii of curvature. 
     
     
       10. The knee replacement prosthesis recited in  claim 9 , wherein the anterior portion of said condylar articulating surfaces has at least a first radius of curvature in the sagittal plane and the posterior portion has at least a first radius of curvature in sagittal plane that is smaller than the first anterior radius of curvature. 
     
     
       11. The knee replacement prosthesis recited in  claim 10 , wherein each of the anterior portion and the posterior portion of the condylar articulating surfaces has multiple radii of curvature in the sagittal plane. 
     
     
       12. The knee replacement prosthesis recited in  claim 10 , wherein the posterior portion of each condylar articulating surface is shaped to allow flexion greater than 100 degrees. 
     
     
       13. The knee replacement prosthesis recited in  claim 1 , wherein said tibial component ( 52 ) comprises a base having distal and proximal surfaces, and a liner having a distal surface that engages the proximal surface of the base and a proximal surface forming said bearing surface that engages and articulates with the femoral component ( 20 ). 
     
     
       14. The knee replacement prosthesis recited in  claim 13 , wherein said base comprises a base plate that rests on the tibial plateau, and a keel fixed to the distal surface of the base plate that can be inserted into the proximal tibial medullary canal. 
     
     
       15. The knee replacement prosthesis recited in  claim 14 , wherein the distal surface of said plate has a textured, roughened surface. 
     
     
       16. The knee replacement prosthesis recited in  claim 1 , wherein anterior and posterior translation of the femoral component ( 20 ) relative to the tibial component ( 52 ) is controlled by the posterior cruciate ligament. 
     
     
       17. The knee replacement prosthesis recited in  claim 1 , wherein tibial rotation is controlled by the posterior cruciate ligament. 
     
     
       18. The knee replacement prosthesis recited in  claim 1 , wherein said femoral component ( 20 ) includes a cam connecting the posterior ends of the condyles, and said tibial component ( 52 ) includes a central post intermediate said concavities. 
     
     
       19. The knee replacement prosthesis recited in  claim 18 , wherein anterior and posterior translation of the femoral component ( 20 ) relative to the tibial component ( 52 ) is controlled by said cam and central post. 
     
     
       20. The knee replacement prosthesis recited in  claim 18 , wherein rotation of the tibia about its longitudinal axis is controlled by said cam and central post. 
     
     
       21. The knee replacement prosthesis recited in  claim 18 , wherein contact between the cam and post occurs at knee flexion greater than about 30 degrees. 
     
     
       22. The knee replacement prosthesis recited in  claim 1 , wherein said patellar surface is substantially defined by non-uniform, rational B-spline. 
     
     
       23. The knee replacement prosthesis recited in  claim 22 , wherein the patellar surface includes a laterally-angled patellar groove and raised trochlear surfaces on each side of the groove. 
     
     
       24. A knee replacement prosthesis having anterior, posterior, lateral, medial, distal and proximal sides and sagittal, coronal and transverse planes, comprising:
 a) a femoral component that connects to the distal end of a resected femur, said femoral component including medial and lateral condyles having distal, articulating surfaces, and a patellar flange having an articulating patellar surface; and, 
 b) a tibial component that connects to the proximal end of a resected tibia, said tibial component including a proximal bearing surface with medial and lateral concavities that articulate with said medial and lateral condyles; 
 wherein said prosthesis enables anterior-posterior translation of the femur relative to the tibia, and 
 wherein said prosthesis restricts axial tibial rotation during initial flexion to an intermediate point and enables axial tibial rotation after the prosthesis has been flexed beyond the intermediate position to full flexion. 
 
     
     
       25. The knee replacement prosthesis recited in  claim 24 , wherein said condylar articulating surfaces and said concavities are substantially defined by non-uniform, rational B-spline surfaces. 
     
     
       26. A knee replacement prosthesis having anterior, posterior, lateral, medial, distal and proximal sides and sagittal, coronal and transverse planes, comprising:
 a) a femoral component that connects to the distal end of a resected femur, said femoral component including medial and lateral condyles having distal, articulating condylar surfaces, and a patellar flange having an articulating patellar surface; and, 
 b) a tibial component that connects to the proximal end of a resected tibia, said tibial component including a proximal bearing surface with medial and lateral concavities that articulate with said medial and lateral condyles; 
 wherein said condylar surfaces and said concavities are substantially defined by high order nonrational B spline surfaces. 
 
     
     
       27. The prosthesis recited in  claim 26 , wherein said patellar flange is substantially defined by high order nonrational B spline surfaces. 
     
     
       28. The prosthesis recited in  claim 27 , wherein said prosthesis enables full flexion of greater than 100 degrees, and enables tibial axial rotation of more than 10 degrees and femoral posterior translation of about 1-2 mm. after full flexion. 
     
     
       29. A method of making a knee replacement prosthesis having anterior, posterior, lateral, medial, distal and proximal sides and sagittal, coronal and transverse planes, comprising the steps of:
 a) a femoral component that connects to the distal end of a resected femur, said femoral component including medial and lateral condyles having distal, articulating surfaces, and a patellar flange having a patellar articulating surface; and, 
 b) a tibial component that connects to the proximal end of a resected tibia, said tibial component including a proximal bearing surface with medial and lateral concavities that articulate with said medial and lateral condyles; 
 c) modeling said condylar surfaces and said concavities using NURBS.